In recent years, an ink jet recording method has found wide application in various kinds of graphic art fields such as photography, various kinds of printing, marking and specific printing such as a color filter because of being able to form images easily and inexpensively. Particularly, it has also become possible to obtain image quality comparable to silver salt photograph images by utilizing a recording apparatus which ejects and controls fine dots, ink in which a color reproduction range, durability and ejection suitability have been improved, and exclusive paper in which ink absorption, color forming property of colorants and surface gloss have been greatly improved. Image quality improvement of an ink jet recording method of today has been achieved only when a complete set of a recording apparatus, ink and exclusive paper is prepared.
However, an ink jet system which requires exclusive paper is problematic in respect to limitation of a recording medium and cost up of a recording medium. Therefore, many attempts have been made which record on a recording medium different from exclusive paper, employing an ink jet recording. Concretely, there are methods such as a phase-conversion ink jet method utilizing wax which is solid at room temperature, a solvent-type ink jet method utilizing an ink which is mainly comprised of a rapid-drying organic solvent and a UV ink jet method in which an ink is cross-linked by ultraviolet (UV) light after recording.
Among them, a UV ink jet method has been noted recently in respect to odor relatively lower than that of a solvent-type ink jet method, rapid drying property and capability of recording on a recording medium having no ink absorption. UV-curable ink jet inks are disclosed, for example, in Japanese Patent Publication No. 5-54667, JP-A (hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection) No. 6-20204 and Japanese Translated PCT Patent Publication No. 2000-504778.
However, even when these inks are employed, the dot diameter of ink ejected onto recording material changes significantly depending on the kind of recording material or operating conditions, and it is therefore impossible to form an image with high resolution on various recording materials.
As UV-curable inks, there are a radical polymerization type UV-curable ink, which is comprised mainly of an acryl composition, and a cation polymerization type UV-curable ink.
The radical polymerization type UV-curable ink has problems in that the polymerization reaction is inhibited by oxygen on account of its polymerization mechanism, resulting in lowering of curability. In contrast, the cation polymerization type UV-curable ink is not influenced by oxygen, however, it has problem in that the polymerization reaction is susceptible to moisture in the molecular level on account of its polymerization mechanism.